(d) force modeling error
(e) propeller shaft velocity (f) propeller shaft velocity error
Fig. 14. Experimental thruster control performance of closed loop
The matching results between simulation with experimental results show excellent correlation with only ±2N error in the entire space of thrust force under various ambient flow velocities and incoming angles. Note that the maximum force of the thrust is up to 50N. The results are also compared with conventional thrust models, and the matching performance with the proposed model is several times better than those of conventional linear ones.
Also in this article, the thrust force control performance of the proposed thruster model was examined. From the results in section 5, the best performance can be obtained by the open loop control with accurate model, because the thrust force cannot be measured directly. This means the force map from the propeller shaft velocity to thrust force plays important roll in control performance. The control performance with the model is acceptable for overall situation, which denoted normally less than ±3N control error.
7. Future works
The thruster modeling and control algorithm need to be enhanced in following aspects.
• Near dead-zone region modeling with complementary experiments
• Dead-zone controller
To precise dynamic positioning control of unmanned underwater vehicles, the dead-zone model and control algorithms should be developed.
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